Download presentation
Presentation is loading. Please wait.
Published byMichael Armstrong Modified over 9 years ago
1
Plant Responses to Internal & External Signals Chapter 39
2
Tropism A plant growth response from hormones that results in the plant growing either toward or away from a stimulus Hormones – chemical messengers that coordinate the different parts of a multicellular organism Types of tropisms: Phototropism – growth toward or away from light Gravitropism – growth toward or away from a gravitational source Thigmotropism – growth toward or away from a touch Vines grow toward a support and then grow toward (around) that support
3
Phototropism video
4
Gravitropism Video
5
Thigmotropism Video
6
Positive v. Negative Tropisms Positive is growth toward a stimulus Positive Phototropism – growth toward light Positive Gravitropism – growth toward a gravitational source Positive Thigmotropism – growth toward a tactile stimulus Negative is growth away from a stimulus Replace the above terms’ “Positive” with “Negative” and then replace “toward” with “away”
7
Hormones Auxins Stimulate cell elongation (remember that zone?) Cause proton pumps to activate Lower pH weakening of cell wall turgor pressure expands & elongates cell wall High concentrations of synthetic auxins KILL certain plants, usually weeds Synthetically produced auxins in high concentration = Herbicides
8
How do you make a …? Cytokinins Stimulate cell division or cytokinesis Proper ratio of auxins & cytokinins cell division & differentiation Gibberellins Work with auxins to stimulate stem elongation Loosen cell walls allowing cellular expansion stem expansion Signal the seed to cease dormancy and germinate Many dwarf plant varieties have non-functional gibberellins
9
Hormones (Page 3) Abscisic acid SLOWS Growth Antagonistic to previously mentioned hormones Promotes seed dormancy, but gibberellins cease it Causes stomata to close to conserve water Ethylene Gas Plays crucial role in programmed cell death (apoptosis) Promotes ripening of fruit Ripening in one fruit ripening in other fruits Positive feedback mechanism = rapid ripening of fruit One bad apple does spoil the lot.
10
Plants respond to Light Plants can detect presence, direction, intensity, and wavelength of light Red & Blue wavelengths are most important Red light is sensed by phytoreceptors Blue light is most important for phototropisms and light-induced opening of stomata Sensed by photoreceptors
11
Phytochromes Photoreceptors for red light (mainly) Exist in 2 isomer forms which can switch forms depending on wavelength available Phytochrome form triggers plant’s developmental responses to light Responsible for Circadian Rhythms 24 hour cycle & not paced by environmental variables Chickens & Summer in Nome, Alaska
12
Photoperiodism Physiological response to a photoperiod (relative lengths of day and night) Night is always the more important of the 2!! But we (humans) focus on the daylight, we’re dumb. Controls Flowering Short-day plants Require a period of continuous darkness exceeding a critical measure in order to flower Early Spring or Fall flowering AP Biology students call them “Long-Night” plants
13
Besides Short-Day plants, Long-Day Plants Flower only if a period of continuous darkness is less than a critical value Flower in Late Spring or early Summer Considered “short-night” plants Day-Neutral Plants No length of continual darkness is needed for flowering
14
Plants respond to things other than light Gravitropism – growth toward or away from light Auxin plays key role If root is plased horizontally, then gravity causes an accumulation of auxins in root’s (radicle’s) lower side Remember HIGH [auxin] = inhibition of growth, so lower side = no growth Upper side = growth Allows the root to grow down into the ground
15
Auxin Accumulation
16
Plants respond to other things… Drought Stomata close Leaves will cease growth Leaves roll into shape that reduces transpiration Deep roots (where H2O is) will speed their growth, but shallow roots will stop growing Predators Thorns, chemicals, distasteful compounds Some plants even attract parasites First layer of defense - Epidermis
17
Coordinated Plant-Parasite Defense
Similar presentations
© 2024 SlidePlayer.com Inc.
All rights reserved.